Best clocks for i5 2500k

Each chip is different. Yours could realistically do anywhere from 4.2 to 5.2Ghz. Most common is 4.4-4.8 you are just going to have to try it to see what yours will do.

So say if i overclocked it to about 4.5 Ghz,would there be any temperature problems
at all?

Not with a Hyper 212+.

My 2500k is at 4.8GHz 1.4v. Temps are under 70c in prime 95.
Edit: I have CM 212+ also.